In the districts of the Old and New Red Sandstone, which include the greater part of Cork and portions of Kerry, Waterford, Tyrone, Fermanagh, Monaghan, Mayo and Tipperary, the soil in the hollows is generally remarkably fertile.

The new kingdom was composed of the present counties of Meath, Westmeath and Longford together with portions of Monaghan, Cavan, King's Co.

At the beginning of the 4th century the three Collas founded the kingdom of Oriel (comprising the present counties of Armagh, Monaghan, north Louth, south Fermanagh) and drove the Ulidians into the eastern part of the province.